1. Technical Field of the Invention
This invention relates generally to portable electronic equipment and more particularly to powering such equipment from low voltage supplies.
2. Description of Related Art
As is known, integrated circuits are used in a wide variety of electronic equipment, including portable, or handheld, devices. Such handheld devices include personal digital assistants (PDA), CD players, MP3 players, DVD players, AM/FM radio, a pager, cellular telephones, computer memory extension (commonly referred to as a thumb drive), etc. Each of these handheld devices includes one or more integrated circuits to provide the functionality of the device. For example, a thumb drive may include an integrated circuit for interfacing with a computer (e.g., personal computer, laptop, server, workstation, etc.) via one of the ports of the computer (e.g., Universal Serial Bus, parallel port, etc.) and at least one other memory integrated circuit (e.g., flash memory). As such, when the thumb drive is coupled to a computer, data can be read from and written to the memory of the thumb drive. Accordingly, a user may store personalized information (e.g., presentations, Internet access account information, etc.) on his/her thumb drive and use any computer to access the information.
As another example, an MP3 player may include multiple integrated circuits to support the storage and playback of digitally formatted audio (i.e., formatted in accordance with the MP3 specification). As is known, one integrated circuit may be used for interfacing with a computer, another integrated circuit for generating a power supply voltage, another for processing the storage and/or playback of the digitally formatted audio data, and still another for rendering the playback of the digitally formatted audio data audible.
Integrated circuits (IC) have enabled the creation of a plethora of handheld devices, however, to be “wired” in today's electronic world, a person needs to possess multiple handheld devices. For example, one may own a cellular telephone for cellular telephone service, a PDA for scheduling, address book, etc., one or more thumb drives for extended memory functionality, an MP3 player for storage and/or playback of digitally recorded music, a radio, etc. Thus, even though a single handheld device may be relatively small, carrying multiple handheld devices on one's person can become quite burdensome.
As integrated circuit technologies evolve, integrated circuit density (i.e., more transistors in smaller die area) is increasing and the supply voltage requirements are decreasing. For example, 0.18 micron CMOS technology has a supply voltage requirement of approximately 1.8 volts. The supply voltage requirements for 0.13 micron and 0.10 micron CMOS technology is even less. With such low supply voltages, standard IC circuits, such as bandgap references, may not operate properly and/or may provide a reference voltage that is too high. For instance, with a supply voltage of 1.8 volts, a desired common mode AC ground for differential signaling would be 0.9 volts. Thus, it would be desirable to have a reference voltage of 0.9 volts as opposed to the traditional 1.2 volts for differential signaling IC circuits such as digital to analog converters, analog to digital converters, operational amplifiers, etc.
Therefore, a need exists for an adjustable bandgap reference to provide an adjustable reference voltage for various low voltage IC circuits.